1. Field of the Invention
This invention is in the field of sensing operating conditions existing in rotating rotary drums which are performing thermal processing.
2. Description of the Prior Art
The need for sophisticated monitoring increases with increasing size of rotary tubular kiln units. Some units employed today have daily outputs of 4,000 metric tons of clinker and more. A careful monitoring is required in order to reduce the number of kiln shutdowns due to lining damage, and thereby reduce the costs. It is particularly important to detect incipient damage at early stages insofar as possible, together with irregularities of material deposits in the inside of the kiln, ring formations, and fractures all of which are manifested by temperature changes of the interior surfaces of the rotary tubular kiln. Experience has shown that suitable countermeasures instituted at an early point in time result in low shutdown times and thus lower production stoppages. Particular problems are involved in the use of complex measuring systems, however, in that the environment in which the rotary kiln is located is normally very dusty and corrosive and is characterized by humidity and vibrations which require the employment of particularly rugged devices which are easy to manipulate.
One of the systems employed for monitoring the temperature of a rotary tubular kiln involves the use of a rugged radiation thermometer which responds slowly and has a large aperture angle. The thermometer is disposed on a rail so as to be displaceable parallel to and at a short distance from the convex surface of the rotary tubular kiln. A detection of the entire surface of the rotary kiln, however, is only achieved after the lapse of a relatively long time interval. Consequently, a rapid perception of incipient lining damage is therefore not readily available.
A further possibility is the disposition of a stationary, pivotable radiation thermometer having a large aperture angle. With a long rotary tubular kiln, however, there is a diminished resolution in the end areas which can be countered only by restricting the scanning angle and, of necessity, employing a plurality of such devices.
An improved detection device for measuring surface temperatures of rotary tubular kilns is disclosed in the publication "AGA Cemscanner, An Infrared System for Real-Time Monitoring of Rotary Kilns" published in 1978. This article suggests measuring devices which have a small aperture angle and a revolving optical system. The measurement is based on a scanning of the surface conducted along a line carried out at such speed that the circumferential speed of the rotary tubular kiln is insignificant in comparison. The emitted radiation thereby proceeds over a rotatably seated prism onto a semiconductor detector which emits an electrical signal corresponding thereto. The device is equipped with a reference radiator which together with the optical system is encapsulated in a steel housing which, in turn, is accommodated in a protective housing which may be climate controlled. The protective housing is disposed in spaced relation from the rotary tubular kiln with the spacing determined by the length of the rotary tubular kiln and the horizontally usable scanning angle. With this device, however, extensive protective measures are necessary in order to protect the highly complex device from the unfavorable environmental conditions in the rotary tubular kiln installation. The device requires a relatively large structural volume and its maintenance requires skilled technical personnel.
The measuring system described in this publication is self-contained and supplies measured values in analog form which are presented as different graphics describing the temperature distribution of the surface of the rotary tubular kiln. The temperature distribution is, in fact, an important parameter of rotary tubular kiln operation. However, the temperature distribution must be interpreted in conjunction with other parameters describing the thermal process or the operation of the rotary tubular kiln such, for example, as the raw material input, the rate of fuel feed, the speed of the drum, the driving power supplied, and the like in order to adjust accurately the metering of raw material and the fuel. A more inclusive evaluation of the identified measured values and their trends are not provided with the system described in this publication.